As is well known in the art, optical fibers include glass base optical fibers using quartz glass and multi-component glass as core and clad components and plastic optical fibers using plastics as core and clad components. As compared with the former, the plastic optical fibers have some drawbacks including an increased transmission loss undesirable for long distance communications, but some advantages including an increase of numerical aperture, ease of handling, and low cost.
Conventional plastic optical fibers generally include cores formed of organic polymers having high light transmittance and clads formed of highly transparent organic polymers having a lower index of refraction than the core polymers. The organic polymers having high light transmittance suitable as the core are typically poly(methyl methacrylate) and polystyrene. It was recently proposed to use organopolysiloxane elastomers as the core material as disclosed in Japanese Patent Application Kokai (JP-A) No. 43613/1985. Advantageously, plastic optical fibers using such elastomer cores have higher flexibility and higher thermal resistance than those using poly(methyl methacrylate) and other conventional core materials.
Nevertheless, the use of organopoly-siloxane elastomers as the optical fiber core has the drawback that external pressure applied to the optical fibers causes the elastomeric cores to deform, resulting in an increased loss of light transmission. It is thus desired to eliminate this drawback.